Circuit board for mounting electronic components

ABSTRACT

In a circuit board wherein a plurality of leads 21 electrically independent of one another protrude from a base member 10, and the respective leads 21 are electrically connected with connection portions 31 of an electronic component 30 mounted on the base member 10; an electronic component mounting circuit board 100 characterized in that internal connection portions 22 are unitarily formed on inner sides of metal members 20 constructing said respective leads 21, that the base members 10 are integrally disposed on both surfaces of said internal connection portions 22, that the electronic components 30 are mounted on said base members 10, and that said electronic components 30 and said internal connection portions 22 are electrically connected. Thus, according to the present invention, it is possible to provide a simply constructed electronic component mounting circuit board which facilitates the design of circuits, which dispenses with the resin molding of the connected portions between the electronic components and the respective leads and affords excellent connection reliability, which can readily form a heat radiating structure, and in which the thermal matching with the electronic components is excellent.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a circuit board for mounting electroniccomponents, and more particularly to a circuit board wherein theconnection portions of an electronic component mounted on a base memberand the corresponding leads protruding from the base member areelectrically connected.

2. Description of the Prior Art

Electronic components which have been highly densified in recent yearscannot alone construct many of the various electronic a available today.Therefore, they are typically packaged on a circuit board. To this end,electronic component mounting circuit boards in various forms haveheretofore been developed and proposed.

There are, for example, three types of connections for connectingelectronic components and terminals to external connections, such asleads, in a circuit board. The first type is, the so-called PGA typewherein a large number of conductor pins planted in a predeterminedarray are connected with the electronic components through conductorcircuits formed on the circuit board. The second type is the so-calledTAB type wherein parts of the conductor circuits on the circuit boardare used as finger leads for directly mounting the electronic componentsthereon. The third type is the so-called DIP type wherein the leads andthe electronic components are connected by wire bonding and then thewhole assembly is molded.

Various concrete devices exemplifying a circuit board of the DIP type,in which a plurality of leads electrically independent of one anotherare protruded from a base member and in which the respective leads andthe connection portions of the electronic components mounted on the basemember are electrically connected, have been proposed in the Japanesepatent application Laid-Open No. 60-194553, etc. Proposed in this laidopen application is:

"A hybrid integrated circuit device characterized in that a circuit baseplate which is made of a material selected from the group consisting ofsilicon, polyimide resin, alumina, epoxy resin, and glass epoxy resin isbonded with adhesives to an island portion of a metallic base ribbon,and in that a circuit element is mounted on said circuit base plate andis molded with a resin." The basic construction of prior-art circuitboards for mounting electronic components as represented by the circuitboard of such a hybrid integrated circuit device can be chieflyclassified into two types as illustrated in FIGS. 1 and 2. The firstbasic construction includes a metal member (the metallic base ribbon)located at a portion (the island portion) on which the electroniccomponent is mounted and being quite independent from a plurality ofother portions that are destined to become leads. The second basicconstruction is related to the first basic construction and is aconstruction wherein the metal member located at a portion for mountingthe electronic component thereon and the plurality of other portionsdestined to become leads are all independent of each other and mustthere be connected by wire bonding.

Prior-art circuit boards of the type in which the connection portions ofthe electronic component mounted on the base member are electricallyconnected with the respective leads must, employ one of the basicconstructions as stated above because the individual leads need to beelectrically independent. Therefore the corresponding terminals of theelectronic component must be respectively connected to these leadsseparately and independently. Also for reasons concerning actualmanufacture, the aforementioned two basic constructions seem to beadopted. More specifically, the electronic component mounting circuitboard as stated above is entirely molded with a resin by so-calledtransfer molding after the predetermined wire bonding has beenperformed, in which case the positioning of the respective leads needsto be easy. To this end, as illustrated in FIG. 2, the leads 21 and themetal member located at the portion (island portion 26) for mounting theelectronic component thereon are formed as a single metal plate by theuse of a frame or the like beforehand, thereby making it possible forthe leads and the metal member located at the island portion to bearranged in the same plane.

With the aforementioned basic construction, however, the followingproblems which must be solved arise in implementing high-densitypackaging which is particularly required of a variety of electroniccomponent mounting circuit boards in recent years:

(1) The leads and those conductor circuits on the base plate to whichthe electronic component is connected must be directly connected by thewire bonding. Therefore, electrodes need to be led out to circuit endportions (the outer peripheral parts of the island portion), not onlybecause the entirety after the mounting of the electronic component ismolded with the resin, but also because the wire bonding is carried outwith short distances. Accordingly, versatility in the design of acircuit becomes very low.

It is also an indispensable condition that the leads be subjected togold or silver plating for reliably performing the wire bonding.

(2) Other than being used as the base of the electronic component, themetal member located at the island portion, namely, the metallic baseribbon located at the island portion, is used merely for forming orreinforcing the electronic component mounting portion, and it cannot bepositively utilized as a wiring circuit. Accordingly, the metallic baseribbon located at the island portion is unsuitable for high-densitypackaging.

(3) In general, an electronic component generates heat when energized,and this heat must be dissipated to the exterior. Nevertheless, in theelectronic component mounting circuit board of the prior art describedbefore, the metal member located underneath the electronic component isnot joined with other metal portions but is embedded in the base member.Therefore, even though the metal member is in the circuit board and isan excellent thermal conductor, it cannot be positively utilized as aheat radiating member.

(4) Since the island portion for mounting the electronic componentthereon and the lead portions to be connected to the exterior arerespectively independent and separate, both can be connected only bywire bonding. Therefore, high-density packaging is difficult, and it isalso required that bonding wire pieces are molded with the resin so asto enhance reliability.

(5) Even if the electronic component and the circuit board side areconnected by solder in some places, the connections of the former to theleads must fundamentally be done by wire bonding. Therefore, a so-calledmolded electronic component for general purposes is difficult to use.

SUMMARY OF THE INVENTION

As a result of earnest research by the inventors in order to solve theproblems described above, it has been discovered that good results areproduced when internal connection portions are unitarily formed insidethe leads and are embedded in a base member constituting a circuitboard, completing the present invention.

Therefore, an object of the present invention is to provide a simplyconstructed electronic component mounting circuit board whichfacilitates circuit design, dispenses with the resin molding of theconnected parts between electronic components and respective leads andaffords excellent connection reliability, can readily form a heatradiating structure, and has excellent thermal matching with theelectronic, components.

Accordingly, the present invention provides a circuit board for mountingat least one electronic component wherein the circuit board comprises asubstrate and several metal members. The substrate includes at least oneinner base member and an outer base member on which the electroniccomponent is mounted. Both the inner base member and the outer basemember have through holes. The metal members are electricallyindependent of one another and protrude from the substrate. Each metalmember includes a lead and an internal connection portion unitarilyformed with the lead. The internal connection portion, which has alarger area than the lead, has first and second services and thesubstrate contacts both surfaces of the internal connection portion. Thecircuit board further comprises conductor circuits between the basemembers. The conductor circuits extend through the internal connectionportions and through the through holes onto the outer base member toelectronically connect the metal members to the electronic component.

Various means employed by the present invention will be detailedly indetail according to the embodiments thereof illustrated in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view showing a prior electroniccomponent mounting circuit board;

FIG. 2 is a plan view of a metallic base ribbon which is used in aprior, electronic component mounting circuit board;

FIG. 3 is a perspective view of an electronic component mounting circuitboard which is the first embodiment of the present invention;

FIG. 4 is a sectional view of the circuit board of the first embodiment;

FIG. 5 is a perspective view of an electronic component mounting circuitboard which is the second embodiment of the present invention;

FIG. 6 is a sectional view of the circuit board of the secondembodiment;

FIG. 7 is a sectional view of an electronic component mounting circuitboard which is the third embodiment of the invention;

FIG. 8 is a sectional view of an electronic component mounting circuitboard which is the fourth embodiment of the present invention;

FIG. 9 is a sectional view of an electronic component mounting circuitboard which is the fifth embodiment of the present invention;

FIG. 10 is a sectional view of an electronic component mounting boardwhich is the sixth embodiment of the present invention; and

FIG. 11 is a plan view of a metallic base ribbon in which a plurality ofmetal members are joined by a frame.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the electronic component mounting circuit board 100 as shown in FIG.3 each electronic component 30 to be mounted thereon is packaged toanother large scale substrate by means of each lead 21 outwardlyextruding from the substrate 10. Each lead 21 employed here is providedinto one body with an internal connection portion 22 embedded into thesubstrate 10. That is, each metal member 20 is constructed of a lead 21and an internal connection portion 22, and such metal members 20 arejointed to a frame 23 as shown in FIG. 11. The substrate 10 is made ofsuitable material such as resin, ceramics and the like, Both surfaces ofthe internal connection portion 22 of each metal member 20 extend insidethe substrate 10, and conductor circuits 11 for electronic components 30are formed onto at least this substrate 10. Each conductor circuit 11 orthe connection portions of the electronic components 30 are electricallyconnected with each internal connection portion 22 or the leads 21 bymeans of through holes 12 or bonding wire pieces 32.

As described above, various materials may be employed for the substrate10, including not only various resins such as silicon, polyimide, epoxy,glassepoxy and the like, but also ceramics such as alumina and the like,provided that they are of insulation and can be securely adhered ontothe internal connection portion 22 made of metal. Further, one bodylaminated substrate of plural material layers may be employed as thesubstrate 10. As shown in FIG. 8, it may be formed onto the metal member20 by printing method and the like. So, each substrate 10 not only canbe formed onto both surfaces of the internal connection portion 22 ofthe metal member 20 and but also, as shown in FIGS. 4, 6, it may beconstructed as a multilayer substrate. Of course, when a multilayersubstrate is employed as the substrate 10, conductor circuits 11 may beformed between respective layers.

Various materials may also be applied for constructing the metal members20. Any metal having the necessary electric conductivity may besatisfactorily employed. for example, copper, iron, a so-called 42 Alloyand the like may be appropriately employed. Because the lead 21 portionof the metal member 20 may be used in the folded condition as shown inFIG. 6 or FIG. 7 or may be used as a radiating fin, it is desirable tochoose the appropriate material. In this connection, the metal member 20mainly made of copper is the most suitable one.

In this electronic component mounting circuit board 100, respectiveelectronic components 30 mounted thereon are connected to the respectiveleads 21 via through holes 12 or bonding wire pieces 32 as describedabove. Accordingly, because the type of electronic components 30employed for this electronic component mounting circuit board 100 isnever limited, either the DIP type of connection or a molded surfacepackaging component such as a chip-on-board may be preferably employed.Further, the electronic components 30 may be mounted on both surfaces ofthis electronic component mounting circuit board 100.

Now, the present invention will be described in detail in conjunctionwith the embodiments illustrated in the drawings.

Embodiment 1

Shown in FIGS. 3 and 4 is the first embodiment of the present invention.In this embodiment, base members 10 are constructed in a multilayerstructure. Conductor circuits 11 are formed, not only on the surfaces ofthe base members 10, but also between the adjacent base members 10. Theinternal connection portions 22 of metal members 20 are embedded in thebase member 10 positioned as the middle layer of the multilayerstructure shown in FIG. 4. The leads 21 are unitary with the respectiveinternal connection portions 22 and protrude outside the base member 10.In addition, the respective leads 21 are bent at right angles to thecorresponding internal connection portions 22 in order that theelectronic component mounting circuit board 100 of the embodiment may bemade as a so-called DIP type wherein it is attached to anotherlarge-sized circuit board, or the like.

Further, in the electronic component mounting circuit board 100, anelectronic component 30 of the DIP type is soldered to the conductorcircuits 11 on the upper surface as viewed in FIG. 4, while anelectronic component 30 of the surface-packaging type is soldered to theconductor circuits 11 on the lower surface.

In an example of the electronic component mounting circuit board 100 ofthe first embodiment, the base members 10 were formed of a glass epoxyresin, and the metal members 20 were formed of a copper-based material.

Embodiment 2

Shown in FIGS. 5 and 6 is the second embodiment of the presentinvention. In this embodiment, as in the first embodiment, base members10 are constructed into a multilayer structure, and conductor circuits11 are formed on the surfaces of these base members 10. Also, theinternal connection portions 22 of metal members 20 are embedded betweenadjacent base members 10, and leads 21 unitary with the respectiveinternal connection portions 22 protrude outside the base members 10.

In the second embodiment, the internal connection portion 22 of themetal member 20 is formed so as to have a somewhat larger area than inthe case of the first embodiment. Thus, each internal connection portion22 is intended to function also as a conductor circuit which is locatedbetween the adjacent base members 10. For that purpose, the internalconnection portion 22 is positively formed with a portion (which maywell be a mere opening) where it is not in direct contact with a throughhole 12.

Also, in the electronic component mounting circuit board 100 of thisembodiment, the internal connection portions 22 of the metal members 20are arranged so as to lie over and under each other within themultilayer structure of the base members 10. More specifically, theelectronic component mounting circuit board 100 is formed using aplurality of sheets (two sheets in this embodiment) in each of which aplurality of metal members 20 are made integral as illustrated in FIG.11. The trains of the leads 21 projecting at the end faces of the basemembers 10 have their levels shifted as shown in FIG. 5.

FIG. 11 is a plan view of a metallic base ribbon in which a plurality ofmetal members 20 are joined by a frame 23. As seen from the figure, eachmetal member 20 is constructed of a lead 21 and an internal connectionportion 22, and such metal members 20 are joined to the frame 23 throughjoint portions 24. In the figure, numeral 25 indicates a cutting linealong which the metallic base ribbon is finally cut.

Further, in the electronic component mounting circuit board 100 of thesecond embodiment, the outer parts of the metal members 20 unitary withthe internal connection portions 22 are bent as shown in FIG. 6, wherebythis circuit board is suited to surface packaging.

In an example of the electronic component mounting circuit board 100 ofthe second embodiment, the base members 10 were formed of a resinousmaterial of a high glass transition point. Thus, an electronic component30 can be connected by pieces of bonding wire 32 to the conductorcircuits 11 located on the surface of the base member 10. That is, inthe electronic component mounting circuit board 100, the electroniccomponent 30 is connected to the conductor circuits 11 on the basemember 10 by wire bonding. In the example, the metal members 20 wereformed of a copper-based material. Further, since the bonding wirepieces 32 are used in this embodiment, at least these bonding wire 32portions need to be molded with a resin or the like.

Embodiment 3

FIG. 7 shows a sectional view of an electronic component mountingcircuit board 100 according to the third embodiment of the presentinvention. The third embodiment is fundamentally the same as the secondembodiment. However, a polyimide film with adhesives is adopted as eachbase member 10, and the internal connection portions 22 of metal members20 are sandwiched between the two base members 10 and are thus bondedand fixed. Also, in order to facilitate the surface packaging of theelectronic component mounting circuit board 100, the fore ends ofrespective leads 21 are bent inwards as illustrated in FIG. 7. In thisexample, a "42 Alloy" was employed for the metal members 20 in thisembodiment.

Embodiment 4

FIG. 8 shows a sectional view of an electronic component mountingcircuit board 100 according to the fourth embodiment of the presentinvention. In this fourth embodiment, the internal, connection portions22 of metal members 20 made of the "42 Alloy" are formed with basemembers 10 by printing or dipping. That is, the base members 10 in thisembodiment are formed to be very thin.

Embodiment 5

FIG. 9 shows a sectional view of an electronic component mountingcircuit board 100 according to the fifth embodiment of the presentinvention. In this circuit board 100, the base member 10 is thinrelative to the internal connection portion 22 of each metal member 20in particular. The material of the metal members 20 is selected inconformity with the type of electronic component 30 to be mounted on thecircuit board 100.

More specifically, if the electronic component 30 is a leadless chipcarrier such as an alumina package, "42 Alloy" is selected as thematerial of the metal members 20, whereby the coefficients of thermalexpansion of the metal members 20 and the electronic component 30 aresubstantially equalized, so as to permit the mounting of the electroniccomponent 30 of this sort and to realize connections of highreliability. Likewise, if the electronic component 30 is a so-calledsilicon chip, the metal members 20 are formed of a copper-cladiron-nickel alloy, whereby the coefficients of thermal expansion of themetal members 20 and the electronic component 30 are substantiallyequalized, so as to permit the mounting of the electronic component 30of this sort and to realize connections of high reliability.

Embodiment 6

FIG. 10 shows a sectional view of an electronic component mountingcircuit board 100 according to the sixth embodiment of the presentinvention. This sixth embodiment is very similar to the secondembodiment, but the former differs from, the latter in that the leadportions of the metal members 20 located above in FIG. 10 are bentupwards whereas to the leads 21 of metal members 20 located below. Theupwardly-bent portions of the metal members 20 are not used as externalconnection terminals but are used as heat radiating portions. Thus, withthis circuit board 100, heat radiation characteristics are excellent.

To sum up, in accordance with the present invention it possible toprovide a simply constructed electronic component mounting circuit board100 which facilitates the design of a circuit, which dispenses with theresin molding of the connected portions between the electroniccomponents and the respective leads and affords excellent connectionreliability, which can readily form a heat radiating structure, and inwhich the thermal matching with the electronic components is excellent.

More specifically, the electronic component mounting circuit board 100has the concrete effects stated below:

(1) Since the respective leads are connected by through holes 12 withconductor circuits 11 located on the base members 10 or conductorcircuits 11 located in the base members 10, the leads and the conductorcircuits 11 on the base members 10 to which the electronic components 10are connected need not be connected directly by wire bonding.Accordingly, it is unnecessary that the conductor circuits 11 be led outto circuit end portions (an island portion) so that the wire bonding canbe realized with short distance. Therefore the circuits can be freelydesigned.

Moreover, since the leads 21 and the conductor circuits 11 on the basemember 10 to which the electronic component 30 is connected need not beconnected directly by wire bonding, the electronic component mountingcircuit board 100 need not always be subject to plating the leads 21.Therefore the circuits can be fabricated easily and inexpensively.

(2) In the electronic component mounting circuit board 100, the metalmembers 20 need not be formed at the portion (island portion) where theelectronic component 30 is mounted. The reasons are that the portion tobe used as the base of the electronic component 30 can be substituted byanother conductor circuit 11, and that strength can be readily ensuredby the internal connection portion 22 of each metal member 20 and thebase member 10 itself.

(3) Heat from the electronic component 30 can be dissipated to theexterior with ease. The internal connection portions 22 of the metalmembers 20 are embedded in the base members 10, and the leads 21 whichare unitary therewith protrude outside the base members 10. Therefore,the metal members 20 which have excellent thermal conductivity can bepositively utilized as heat radiating members.

(4) Since the respective conductor circuits 11 and leads 21 can beconnected through corresponding through holes 12, the electricalreliability of the connections can be rendered very high. Moreover, itis possible to form a large number of through holes 12. Therefore, eachelectronic component 30 can satisfactorily endure even comparativelylarge currents flowing therethrough, and the range of applications ofthe circuit board of the invention can be widened much more than that ofthe prior-art circuit board wherein the conductor circuits and the leadsare connected only by wire bonding which uses fine metallic wire.

(5) Owing to a structure in which the respective conductor circuits 11and leads 21 are connected through corresponding through holes 12, thebase members 10 as well as the conductor circuits 11 can besatisfactorily brought into a multilayer assembly, and the structure ofthe portion where the electronic component 30 is mounted can be alteredat will. In the electronic component mounting circuit board 100,therefore, the type of electronic component 30 to be mounted does notcome into question at all, and packaging at a sufficient high densitycan be implemented.

What is claimed is:
 1. A circuit board for mounting at least oneelectronic component, the circuit board comprising:a substrate includingat least one inner base member and an outer base member on which the atleast one electronic component is mounted said base member havingthrough holes; a plurality of metal members which are electricallyindependent of one another and which protrude from the substrate, eachmetal member including a lead and an internal connection portionunitarily formed with the lead and having a larger area than the leadand first and second surfaces, the substrate contacting both surfaces ofthe internal connection portion; and conductor circuits between saidbase members extending through the internal connection portions andthrough the through holes onto the outer base member to electricallyconnect the metal members to the at least one electronic component.
 2. Acircuit board for mounting at least one electronic component as definedin claim 1 wherein said internal connection portions of said respectiveleads are arranged in a state in which they lie over and under eachother.